The present disclosure relates generally to media pick and separation systems that are used in image forming devices, such as printers, copiers, facsimile machines and the like. These types of image forming devices typically include a feed mechanism that supplies individual sheets of print media (e.g. paper) onto which images are formed. Many such image forming devices include a tray that stores an input stack of sheets of print media, and a pick mechanism is used to pick the top sheet off of the input stack and advance the sheet to the feed mechanism.
One type of pick mechanism includes a rotating pre-pick roller that is attached to an end of a pick arm. The pre-pick roller is brought into and out of engagement with the top of the stack at an appropriate time through rotation of the pick arm. Upon contacting the top of the input stack, the pre-pick roller frictionally engages the top sheet on the stack and urges the sheet forward to the pick roller and the other portions of the feed mechanism.
During the pick process, it is desirable to maintain the magnitude of the normal force exerted onto the stack by the pre-pick roller within a predefined range so that the pre-pick roller will properly engage the top sheet in the stack. If the magnitude of the normal force is too low, the pick roller will not be able to frictionally engage the top sheet. If the magnitude of the normal force is too high, multiple sheets may be fed and back tension can be created. Additionally, the mechanism that rotates the pick arm can impose a parasitic drag on the printer system, which places a drag on motor torque.